U.S. patent application number 15/325517 was filed with the patent office on 2017-06-15 for motor.
The applicant listed for this patent is Panasonic Intellectual Property Managemnet Co., Ltd.. Invention is credited to HARUHIKO KADO, TAKASHI OGAWA, YUKIHIRO OKADA, YUSUKE OKUMURA, YUICHI YOSHIKAWA.
Application Number | 20170170696 15/325517 |
Document ID | / |
Family ID | 55532778 |
Filed Date | 2017-06-15 |
United States Patent
Application |
20170170696 |
Kind Code |
A1 |
OGAWA; TAKASHI ; et
al. |
June 15, 2017 |
MOTOR
Abstract
Motor according to the present invention includes rotor core and
rotor. Rotor core includes outer circumferential surface formed
along shaft center, and a plurality of magnet holes. Each of magnet
holes has a convex surface located on a side of rotary shaft and a
concave surface located on a side of outer circumferential surface.
.alpha.1 is a distance between the convex surface and the concave
surface on an end part located on the side of outer circumferential
surface. .beta.1 is a distance between the convex surface and the
concave surface on a central part located on the side of rotary
shaft. In magnet hole, .alpha.1 is larger than .beta.1. Bonded
magnets are filled in magnet holes. .alpha.2 is a thickness of a
magnet component located on the end part in an oriented direction
of the magnet component. .beta.2 is a thickness of a magnet
component located on the central part in an oriented direction of
the magnet component. In each of the plurality of bonded magnets,
.alpha.2 is larger than .beta.2.
Inventors: |
OGAWA; TAKASHI; (Osaka,
JP) ; YOSHIKAWA; YUICHI; (Osaka, JP) ; KADO;
HARUHIKO; (Osaka, JP) ; OKADA; YUKIHIRO;
(Osaka, JP) ; OKUMURA; YUSUKE; (Osaka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Managemnet Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
55532778 |
Appl. No.: |
15/325517 |
Filed: |
September 2, 2015 |
PCT Filed: |
September 2, 2015 |
PCT NO: |
PCT/JP2015/004451 |
371 Date: |
January 11, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K 1/2773 20130101;
H02K 29/03 20130101; H02K 2213/03 20130101; H02K 1/2766 20130101;
H02K 21/14 20130101; H02K 15/03 20130101 |
International
Class: |
H02K 1/27 20060101
H02K001/27; H02K 29/03 20060101 H02K029/03; H02K 21/14 20060101
H02K021/14 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 16, 2014 |
JP |
2014-187368 |
Claims
1. A motor comprising: a stator including: a winding through which
a drive current flows; and a stator core around which the winding
is wound; and a rotor including: a rotary shaft; a rotor core which
is mounted to the rotary shaft to form a columnar body in a
direction of a shaft center of the rotary shaft, and includes an
outer circumferential surface formed along the shaft center and a
plurality of magnet holes located along the outer circumferential
surface, each of the magnet holes having: a convex surface located
on a side of the rotary shaft; and a concave surface located on a
side of the outer circumferential surface, each of the magnet holes
having a shape of projecting from the outer circumferential surface
toward a position where the rotary shaft is located, and being
configured such that a distance .alpha.1 between the convex surface
and the concave surface on an end part of the magnet hole located
on the side of the outer circumferential surface is larger than a
distance .beta.1 between the convex surface and the concave surface
on a central part of the magnet hole located on the side of the
rotary shaft; and each of a plurality of bonded magnets which is
filled in each of the plurality of magnet holes, and formed such
that a thickness .alpha.2 of a magnet component located on the end
part in an oriented direction is larger than a thickness .beta.2 of
a magnet component located on the central part in an oriented
direction, wherein the rotor has: a plurality of d-axis magnetic
flux paths that generates magnet torque, out of rotary torques
generated on the rotor due to a rotating magnetic field generated
by the stator, when the drive current flows through the winding;
and a plurality of q-axis magnetic flux paths that generates
reluctance torque out of the rotary torques, wherein each of the
d-axis magnetic flux paths is located to cross each of the
plurality of bonded magnets, and each of the q-axis magnetic flux
paths is located along each of the plurality of bonded magnets.
2. The motor according to claim 1, wherein, in each of the
plurality of bonded magnets, a density of the magnet located on the
end part is lower than a density of the magnet located on the
central part.
3. The motor according to claim 1, wherein the bonded magnets are
filled in the plurality of magnet holes through an insert die, and
when a density of one of the bonded magnet filled in a point P1 is
defined as X, a distance from a point P2 where a gate included in
the insert die is located to the point P1 is defined as Y, and a
theoretical material density of the bonded magnet is defined as C,
a decrease rate A of a density of the bonded magnet is represented
by A=X/(Y.times.C), and the thickness .beta.2 satisfies
.beta.2=A.times..alpha.2.
4. The motor according to claim 1, wherein, in each of the bonded
magnets, resistance to demagnetization D1 of a magnet central part
located on the central part and resistance to demagnetization D2 of
a magnet end part located on the end part are equal to each
other.
5. The motor according to claim 1, wherein each of the plurality of
magnet holes has an arc shape of projecting from the outer
circumferential surface toward a position where the rotary shaft is
located, and a radius R1 forming an arc included in the concave
surface is smaller than a radius R2 forming an arc included in the
convex surface.
6. The motor according to claim 5, wherein the arc included in the
concave surface has two or more different curvatures.
Description
TECHNICAL FIELD
[0001] The present invention relates to a motor including an
interior permanent magnet rotor provided with a plurality of
permanent magnets in a rotor core.
BACKGROUND ART
[0002] Conventionally, a motor using a permanent magnet includes a
rotor provided on an inner circumference of a stator with a gap
interposed between the rotor and the stator.
[0003] The stator has substantially a cylindrical shape, and
generates a rotating magnetic field.
[0004] The rotor includes a rotary shaft and a rotor core. The
rotor rotates around the rotary shaft. A magnet hole into which a
permanent magnet is inserted is formed on the rotor core. A
magnetic pole is formed on the rotor by the permanent magnet
inserted into the rotor core.
[0005] A motor in which a permanent magnet is embedded into a rotor
core as in the configuration described above is also referred to as
an interior permanent magnet (IPM) motor.
[0006] A small piece of an Nd--Fe--B sintered magnet or a small
piece of a ferrite sintered magnet has been widely used for a
permanent magnet.
[0007] In the case where a small piece of a permanent magnet is
used, a magnet hole formed on a rotor core is formed with a size
slightly larger than the outer shape of the small piece of the
permanent magnet. If the magnet hole has a size slightly larger
than the outer shape of the small piece of the permanent magnet,
workability in assembling the rotor is enhanced. The reason of the
enhancement in workability is as stated below.
[0008] Specifically, the magnet hole formed on the rotor core is
formed through a process for working a metal. The process for
working a metal is referred to as a metal working process below.
Therefore, the magnet hole is formed with high-precise working, and
thus, a dimensional tolerance is small.
[0009] On the other hand, the small piece of the permanent magnet
described above is formed through a process for sintering magnet
powders or the like. The process for sintering magnet powders or
the like is referred to as a sintering process below. The sintering
process is similar to a process for firing ceramics or the like in
a kiln. Accordingly, a small piece of a permanent magnet which has
been subjected to the sintering process may sometimes be deformed,
for example, may be warped or bent. If the small piece of the
permanent magnet is subjected to a process for grinding the small
piece with a grind stone or the like, the deformation occurring on
the small piece of the permanent magnet can be eliminated. The
process for grinding the small piece with a grind stone or the like
is referred to as a grinding process below.
[0010] A motor does not employ a grinding process for eliminating
deformation on a small piece of a permanent magnet. Alternatively,
even if a grinding process is employed for a motor, an amount to be
ground of a small piece of a permanent magnet is very small. In
addition, precision in grinding a small piece of a permanent magnet
is low.
[0011] Accordingly, as described above, a motor addresses
deformation on a small piece of a permanent magnet by setting a
magnet hole to be slightly larger than the outer shape of the small
piece of the permanent magnet. It is to be noted that, when the
grinding process is employed, the following problems arise.
Specifically, the problems include the need of facility and an
increase in the number of working processes.
[0012] However, in the case where the magnet hole is set to be
slightly larger than the outer shape of the small piece of the
permanent magnet, a gap is generated between the rotor core and the
small piece of the permanent magnet. The gap between the rotor core
and the small piece of the permanent magnet acts as magnetic
resistance. Therefore, magnetic flux density generated on the
surface of the rotor decreases.
[0013] Further, a small piece of a permanent magnet formed from an
Nd--Fe--B sintered magnet or a ferrite sintered magnet has
characteristics of being hard and fragile, like ceramics. In view
of this, a small piece of a permanent magnet cannot be formed to
have a complex shape.
[0014] Specifically, the following shape is employed for a small
piece of a permanent magnet. That is, a small piece of a permanent
magnet is a columnar body with a rectangular cross-section. The
columnar body with a rectangular cross-section is a planar plate.
Alternatively, a small piece of a permanent magnet is a columnar
body with a trapezoidal cross-section. A small piece of a permanent
magnet is a columnar body with an arc cross-section. The columnar
body with an arc cross-section is a plate having substantially a U
shaped cross section.
[0015] Any of the small pieces of permanent magnets formed through
the above molding process has a large dimension tolerance.
Therefore, when the small pieces of the permanent magnets are used,
a gap is formed between the rotor core and the used small piece of
the permanent magnet.
[0016] To address this problem, PTL 1 discloses an interior
permanent magnet rotor including a bonded magnet in a magnet hole.
The bonded magnet is formed by filling a mixture constituting the
bonded magnet into the magnet hole. The mixture constituting the
bonded magnet includes magnet powders, resin material, and a small
amount of additives. The mixture constituting the bonded magnet is
used in the state in which magnet powders, resin material, and a
small amount of additives are melted. The bonded magnet is molded
in such a way that, after the mixture constituting the bonded
magnet is filled in the magnet hole, a process such as a
pressurizing process is performed. The process for molding the
bonded magnet is referred to as a molding process below.
[0017] Particularly in the case where thermosetting resin is used
as the resin material, the molding process includes the following
processes. Specifically, the molding process includes a heating
process for heating the mixture and melting the heated mixture.
Since a thermosetting reaction is caused in the heated mixture, the
mixture is cured. The cured mixture is cooled through a cooling
process. The cooled mixture constitutes the bonded magnets.
[0018] In addition, in the case where thermoplastic resin is used
as the resin material, the molding process includes the following
processes. Specifically, the molding process includes a heating
process for heating the mixture and melting the heated mixture. The
heated mixture is cooled through a cooling process. The cooled
mixture is re-cured to constitute the bonded magnets.
[0019] Note that, in the description below, a mixture constituting
a bonded magnet is also referred to as a bonded magnet in some
cases.
[0020] According to this configuration, the bonded magnet is filled
without a gap along the shape of the magnet hole formed on the
rotor core. Since there is no gap generated between the rotor core
and the bonded magnet, the reduction in a magnetic flux generated
on the rotor is suppressed.
[0021] Further, PTL 2 discloses a manufacturing method of an
interior permanent magnet rotor using an insert die having a
plurality of gates. The gate is an inlet opening from which a
bonded magnet is inserted. In PTL 2, a mixture constituting a
bonded magnet is inserted from both ends of a magnet hole using the
above-mentioned insert die.
CITATION LIST
Patent Literature
[0022] PTL 1: Unexamined Japanese Patent Publication No.
H10-304610
[0023] PTL 2: Unexamined Japanese Patent Publication No.
2013-121240
SUMMARY OF THE INVENTION
[0024] A motor according to the present invention includes a stator
and a rotor.
[0025] The stator includes a winding through which a drive current
flows and a stator core around which the winding is wound.
[0026] The rotor includes a rotary shaft, a rotor core, and a
plurality of bonded magnets.
[0027] The rotor core is mounted to the rotary shaft to form a
columnar body in a direction of a shaft center of the rotary shaft.
The rotor core includes an outer circumferential surface formed
along the shaft center, and a plurality of magnet holes. Each of
the plurality of magnet holes is located along the outer
circumferential surface. Each of the plurality of magnet holes has
a convex surface located on a side of the rotary shaft and a
concave surface located on a side of the outer circumferential
surface. Each of the plurality of magnet holes has a shape of
projecting from the outer circumferential surface toward a position
where the rotary shaft is located. Here, .alpha.1 is a distance
between the convex surface and the concave surface on an end part
located on the side of the outer circumferential surface. .beta.1
is a distance between the convex surface and the concave surface on
a central part located on the side of the rotary shaft. In each of
the plurality of magnet holes, .alpha.1 is larger than .beta.1.
[0028] Each of the plurality of bonded magnets is filled in each of
the magnet holes. Here, .alpha.2 is a thickness of a magnet
component located on the end part in an oriented direction of the
magnet component. .beta.2 is a thickness of a magnet component
located on the central part in an oriented direction of the magnet
component. In each of the plurality of bonded magnets, .alpha.2 is
larger than .beta.2.
[0029] In addition, the rotor has a plurality of d-axis magnetic
flux paths and a plurality of q-axis magnetic flux paths. A
plurality of d-axis magnetic flux paths generates magnet torque out
of rotary torques generated on the rotor due to a rotating magnetic
field generated by the stator, when a drive current flows through
the winding. Similarly, a plurality of q-axis magnetic flux paths
generates reluctance torque out of rotary torques.
[0030] Each of the d-axis magnetic flux paths is located to cross
each of the plurality of bonded magnets. Each of the q-axis
magnetic flux paths is located along each of the plurality of
bonded magnets.
BRIEF DESCRIPTION OF DRAWINGS
[0031] FIG. 1 is a perspective assembly view of a main part
constituting a motor according to an exemplary embodiment of the
present invention.
[0032] FIG. 2 is a flowchart illustrating an assembly process of
the main part constituting the motor according to the exemplary
embodiment of the present invention.
[0033] FIG. 3 is a sectional view illustrating the motor according
to the exemplary embodiment of the present invention.
[0034] FIG. 4 is an explanatory view for describing a path of a
magnetic flux generated on a rotor used in the motor according to
the exemplary embodiment of the present invention.
[0035] FIG. 5 is an enlarged view of a key part of the motor
illustrated in FIG. 3.
[0036] FIG. 6 is another enlarged view of the key part of the motor
illustrated in FIG. 3.
[0037] FIG. 7 is another enlarged view of the key part of the motor
illustrated in FIG. 3.
[0038] FIG. 8 is a sectional view along line 8-8 in FIG. 7.
[0039] FIG. 9 is another enlarged view of the key part of the motor
illustrated in FIG. 3.
[0040] FIG. 10 is a graph illustrating characteristics relating to
a distance of a mixture constituting a bonded magnet filled in a
magnet hole from a gate position and a density of a cured bonded
magnet in the interior permanent magnet rotor used in the motor
according to the exemplary embodiment of the present invention.
DESCRIPTION OF EMBODIMENT
[0041] A motor according to the exemplary embodiment of the present
invention can suppress deterioration in magnetic characteristics at
low cost without increasing the size of the motor by the
configuration described below.
[0042] Specifically, there is the problem described below in
employing the bonded magnet disclosed in PTL 1 in an interior
permanent magnet rotor used in a conventional motor by using the
manufacturing method disclosed in PTL 2. That is, a mixture filled
in each of magnet holes from both ends thereof to constitute a
bonded magnet generates a flow toward the central part of each
magnet hole. The mixture filled from both ends of each magnet hole
forms a weld on the location where the flows of the bonded magnet
merge. The mixture cured through a molding process constitutes the
bonded magnet in the state of including the weld. Therefore, in the
bonded magnet manufactured by the manufacturing process described
above, the magnetic characteristics are deteriorated on the central
part of the magnet hole where the weld occurs.
[0043] In view of this, the motor according to the exemplary
embodiment of the present invention is configured to allow a
mixture constituting a bonded magnet to easily flow by the
configuration described below, thereby being capable of suppressing
the reduction in the density of the bonded magnet. Therefore, even
if a mixture constituting a bonded magnet is filled from a central
part of a magnet hole, the motor can suppress deterioration in
magnetic characteristics of the bonded magnet on an end part of the
magnet hole.
[0044] In addition, in the motor according to the exemplary
embodiment of the present invention, only a thickness .alpha.2 on a
magnet end part, which is located on a position distant from a
position where a gate is located and which is included in the
bonded magnet, is set large. The present configuration can prevent
a large increase in an amount of a material to be used for forming
a bonded magnet. Thus, an inexpensive motor can be provided without
increasing the size of the motor.
[0045] An exemplary embodiment of the present invention will be
described below with reference to the drawings. Note that the
exemplary embodiment described below is merely illustrative of
implementing the present invention, and not restrictive of the
technical scope of the present invention.
EXEMPLARY EMBODIMENT
[0046] FIG. 1 is a perspective assembly view of a main part
constituting a motor according to an exemplary embodiment of the
present invention. FIG. 2 is a flowchart illustrating an assembly
process of the main part constituting the motor according to the
exemplary embodiment of the present invention.
[0047] In addition, FIG. 3 is a sectional view illustrating the
motor according to the exemplary embodiment of the present
invention. FIG. 4 is an explanatory view for describing a path of a
magnetic flux generated on a rotor used in the motor according to
the exemplary embodiment of the present invention. FIG. 5 is an
enlarged view of a key part of the motor illustrated in FIG. 3.
FIGS. 6, 7, and 9 are each another enlarged view of the key part of
the motor illustrated in FIG. 3. FIG. 8 is a sectional view along
line 8-8 in FIG. 7.
[0048] In addition, FIG. 10 is a graph illustrating characteristics
relating to a distance of a mixture constituting a bonded magnet
filled in a magnet hole from a gate position and a density of a
cured bonded magnet in the interior permanent magnet rotor used in
the motor according to the exemplary embodiment of the present
invention.
[0049] Firstly, one example of a process of assembling motor 100
according to the exemplary embodiment of the present invention will
briefly be described with reference to FIGS. 1 and 2.
[0050] As illustrated in FIG. 1, motor 100 according to the present
exemplary embodiment includes interior permanent magnet rotor 10
and stator 40. In the description below, interior permanent magnet
rotor 10 is merely referred to as rotor 10 in some cases.
[0051] As illustrated in FIG. 2, rotor 10 and stator 40 are
simultaneously prepared.
[0052] Firstly, rotor core 11 is prepared for rotor 10 (S1). Thin
steel plates constituting rotor core 11 are punched by a die. Each
of the steel plates is punched by a die to form a magnet hole.
Rotary shaft 12 is inserted into each of a plurality of steel
plates punched out by the die. The plurality of steel plates is
laminated along the shaft center of rotary shaft 12 to form rotor
core 11.
[0053] Then, a mixture constituting a bonded magnet is filled in a
magnet hole formed on rotor core 11 (S2). The mixture constituting
the bonded magnet is used in the state in which magnet powders,
resin material, and a small amount of additives are melted. The
mixture constituting the bonded magnet is filled in the magnet hole
from a gate included in an insert die.
[0054] The mixture filled in rotor 10 is cured through a molding
process to constitute a bonded magnet. During the molding process,
a process according to the characteristic of the resin material
included in the mixture is performed (S3).
[0055] On the other hand, stator core 41 is prepared for stator 40
(S4). As in rotor core 11, stator core 41 is formed by laminating
thin steel plates. Insulator 42 which is an insulating member is
attached to stator core 41 (S5).
[0056] Next, a winding 43 through which a current is to flow is
wound around stator core 41 to which insulator 42 is attached
(S6).
[0057] Rotor 10 and stator 40, which are individually prepared, are
combined to each other (S7). As illustrated in FIG. 3, motor 100
according to the present exemplary embodiment includes rotor 10
inserted into stator 40 on an inner circumferential side with a gap
interposed between rotor 10 and stator 40. The main part of motor
100 will be described later. As illustrated in FIG. 1, when rotor
10 is inserted into stator 40, a pair of bearings 30 is attached to
rotary shaft 12 of rotor 10. Rotor 10 is rotatably supported by a
pair of bearings 30.
[0058] Next, the motor according to the exemplary embodiment of the
present invention will be described in detail with reference to
FIGS. 3 to 10. In the description below, an interior permanent
magnet rotor is employed as the rotor as one example.
[0059] As illustrated in FIG. 3, motor 100 according to the present
exemplary embodiment includes stator 40 and rotor 10.
[0060] Stator 40 includes winding (43) through which a drive
current flows and stator core 41 around which winding (43) is
wound.
[0061] Rotor 10 includes rotary shaft 12, rotor core 11, and a
plurality of bonded magnets 14.
[0062] Rotor core 11 is mounted to rotary shaft 12 to form a
columnar body in a direction of shaft center 12a of rotary shaft
12. Rotor core 11 includes outer circumferential surface 11b formed
along shaft center 12a, and a plurality of magnet holes 13. Each of
the plurality of magnet holes 13 is located along outer
circumferential surface 11b.
[0063] As illustrated in FIG. 5, each of the plurality of magnet
holes 13 has convex surface 17a located on the side of rotary shaft
12 and concave surface 18a located on the side of outer
circumferential surface 11b. Each of the plurality of magnet holes
13 has a shape of projecting from outer circumferential surface 11b
toward the position where rotary shaft 12 is located. Here,
.alpha.1 is a distance between convex surface 17a and concave
surface 18a on end part 15a located on the side of outer
circumferential surface 11b. .beta.1 is a distance between convex
surface 17a and concave surface 18a on central part 16a located on
the side of rotary shaft 12. In each of the plurality of magnet
holes 13, .alpha.1 is larger than .beta.1.
[0064] Each of the plurality of bonded magnets 14 is filled in each
of the plurality of magnet holes 13. Here, .alpha.2 is a thickness
of a magnet component located on end part 15a in an oriented
direction of the magnet component. .beta.2 is a thickness of a
magnet component located on central part 16a in an oriented
direction of the magnet component. In each of the plurality of
bonded magnets 14, .alpha.2 is larger than .beta.2.
[0065] In addition, as illustrated in FIG. 4, rotor 10 has a
plurality of d-axis magnetic flux paths 20 and a plurality of
q-axis magnetic flux paths 21. The plurality of d-axis magnetic
flux paths 20 generates magnet torque out of rotary torques
generated on rotor 10 due to a rotating magnetic field generated by
stator 40, when a drive current flows through windings (43).
Similarly, the plurality of q-axis magnetic flux paths 21 generates
reluctance torque out of rotary torques.
[0066] Each of d-axis magnetic flux paths 20 is located to cross
each of the plurality of bonded magnets 14. Each of q-axis magnetic
flux paths 21 is located along each of the plurality of bonded
magnets 14.
[0067] Notably, in the present exemplary embodiment, bonded magnets
14 are filled in magnet holes 13. Therefore, .alpha.1 and .beta.1
indicating the thickness of magnet hole 13 and .alpha.2 and .beta.2
indicating the thickness of bonded magnet 14 have substantially the
following relation. That is, .alpha.1=.alpha.2 and .beta.1=.beta.2
are established.
[0068] The motor providing particularly significant operation and
effects is as stated below.
[0069] Specifically, as illustrated in FIGS. 3 and 5, in each of
the plurality of bonded magnets 14, the density of the magnet on
end part 15a is lower than the density of the magnet on central
part 16a.
[0070] In addition, as illustrated in FIG. 9, bonded magnet 14 is
further filled in each of the plurality of magnet holes 13 through
an insert die. Bonded magnet 14 satisfies the following condition.
Specifically, the density of bonded magnet 14 filled in point P1 is
defined as X. The distance from point P2 where gate 50 included in
the insert die is located to point P1 is defined as Y. The
theoretical material density of bonded magnet 14 is defined as C.
In this case, the decrease rate A of the density of bonded magnet
14 is represented by A=X/(Y.times.C). Further, in bonded magnet 14,
thickness .beta.2 of the magnet component located on magnet central
part 16 in the oriented direction satisfies
.beta.2=A.times..alpha.2. This configuration will be described
later in detail.
[0071] In addition, as illustrated in FIG. 5, in bonded magnet 14,
resistance to demagnetization D1 of magnet central part 16 located
on central part 16a and resistance to demagnetization D2 of magnet
end part 15 located on end part 15a are equal to each other.
Notably, the state in which resistance to demagnetization D1 and
resistance to demagnetization D2 are equal to each other means that
they are equal to each other in practical usage. In other words,
the state described above does not mean only the case where
resistance to demagnetization D1 and resistance to demagnetization
D2 exactly match each other. This configuration will be described
later in detail.
[0072] Further, as illustrated in FIG. 5, each of the plurality of
magnet holes 13 has an arc shape of projecting from outer
circumferential surface 11b toward the position where rotary shaft
12 is located. In each of magnet holes 13, radius R1 of arc 18
included in concave surface 18a is shorter than radius R2 of arc 17
included in convex surface 17a.
[0073] In addition, as illustrated in FIG. 6, arc 18 included in
concave surface 18a has two or more different curvatures 1/R1a and
1/R1b.
[0074] The interior permanent magnet rotor used in the motor
according to the present exemplary embodiment will be described in
more detail with reference to the drawings.
[0075] As illustrated in FIGS. 1 and 3, motor 100 includes rotor 10
and stator 40. Stator 40 has teeth 44 extending toward shaft center
12a of rotary shaft 12. Windings 43 are wound around teeth 44 of
stator 40. A core wire including any one of copper, copper alloy,
aluminum, and aluminum alloy can be used for a core wire included
in each of windings 43.
[0076] Rotor 10 includes rotor core 11, a plurality of magnet holes
13, and a plurality of bonded magnets 14. Rotor core 11 is formed
by laminating steel plates 11a, which are punched out, in the
direction of shaft center 12a of rotary shaft 12. Mixture (14a)
constituting bonded magnets 14 is filled in magnet holes 13.
[0077] As illustrated in FIGS. 3 and 5, each bonded magnet 14 has
an arc shape in which magnet central part 16 projects toward rotary
shaft 12. Bonded magnet 14 has magnet end part 15 near outer
circumferential surface 11b of rotor core 11. On magnet end part
15, the thickness of the magnet component in the oriented direction
thereof is .alpha.2. On magnet central part 16, the thickness of
the magnet component in the oriented direction thereof is .beta.2.
The thickness in the oriented direction of the magnet component is
also referred to as a magnet thickness below. Magnet thickness
.alpha.2 and magnet thickness .beta.2 have the relation of
.alpha.2>.beta.2.
[0078] As illustrated in FIG. 5, bonded magnets 14 used in rotor 10
according to the present exemplary embodiment are configured as
described below to establish the relation of .alpha.2>.beta.2.
Specifically, in each of bonded magnets 14, radius R1 of arc 18
included in concave surface 18a is shorter than radius R2 of arc 17
included in convex surface 17a.
[0079] Notably, as illustrated in FIG. 6, magnet thicknesses
.alpha.2 and .beta.2 can freely be set in bonded magnets 14 used in
rotor 10 in the present exemplary embodiment according to the
configuration described below.
[0080] Specifically, in each bonded magnet 14, the radius of arc 18
included in concave surface 18a includes two or more different
curvatures 1/R1a and 1/R1b. That is, the radius of arc 18 included
in concave surface 18a is formed by connecting arcs having
different curvatures of 1/R1a and 1/R1b to each other.
[0081] Meanwhile, in the case where a mixture constituting a bonded
magnet is filled from a central part of a magnet hole using a gate
included in an insert die, problems described below may arise.
[0082] Specifically, there may be the case where the density of the
bonded magnet obtained by curing the mixture constituting the
bonded magnet is different between the location near the gate from
which the mixture is inserted and the location distant from the
gate. That is, the result similar to the case where the filling
pressure for the mixture constituting the bonded magnet is lowered
is obtained on the location distant from the gate, that is, on the
magnet end part.
[0083] Consequently, the bonded magnet obtained by curing the
mixture may have deterioration in magnetic characteristics on the
portion having low density.
[0084] In view of this, as illustrated in FIGS. 7 and 8, the rotor
used in the motor according to the present exemplary embodiment
employs the configuration described below. Specifically, in magnet
hole 13, a width of magnet end part 15 located on end part 15a is
larger than a width of magnet central part 16 located on central
part 16a.
[0085] According to this configuration, mixture 14a constituting
bonded magnets 14 is filled in magnet holes 13 from gate 50
included in an insert die. In the present exemplary embodiment,
mixture 14a constituting bonded magnets 14 is filled from central
part 16a of each magnet hole 13. Mixture 14a to be filled to
constitute bonded magnets 14 includes magnet powders, resin
material, and a plurality of additives.
[0086] In this case, in rotor 10, magnet thickness .alpha.2 on
magnet end part 15 located on end part 15a distant from gate 50 is
larger than magnet thickness .beta.2 on magnet central part 16
located on central part 16a where gate 50 is provided. Therefore,
mixture 14a constituting bonded magnets 14 is easy to flow on end
part 15a. Accordingly, the variation in density of mixture 14a
constituting bonded magnets 14 is reduced more than conventionally
in the region from central part 16a of magnet hole 13 to end part
15a of magnet hole 13. Since the variation in density of mixture
14a is reduced, an extreme density variation does not occur on
bonded magnet 14 obtained by curing mixture 14a. Consequently, in
bonded magnet 14, local deterioration in magnetic characteristics
is not caused.
[0087] In addition, in the present configuration, only magnet
thickness .alpha.2 on magnet end part 15 distant from gate 50 is
set larger. Thus, the amount of the material to be used to
constitute bonded magnet 14 can be decreased, in addition to the
above-mentioned operation and effect. Accordingly, rotor 10
according to the present exemplary embodiment can suppress
deterioration in magnetic characteristics at low cost without
increasing the size of motor 100.
[0088] Specifically, the rotor used in the motor according to the
present exemplary embodiment is configured to satisfy the following
relation. That is, the decrease rate of the density of bonded
magnet 14 is defined as A. In this case, bonded magnet 14 satisfies
equation (1) with respect to magnet thickness .alpha.2 on magnet
end part 15 and magnet thickness .beta.2 on magnet central part
16.
.beta.2=A.times..alpha.2 (1)
[0089] Here, decrease rate A indicating the density of bonded
magnet 14 is represented by the following equation. That is, as
illustrated in FIG. 9, the density of bonded magnet 14 to be filled
on arbitrary point P1 of magnet hole 13 is defined as X. The
distance from point P2 where gate 50 is located to arbitrary point
P1 is defined as Y. The theoretical material density of bonded
magnet 14 is defined as C. In this case, decrease rate A is
represented by equation (2).
A=X/(Y.times.C) (2)
[0090] Then, as illustrated in FIG. 8, mixture 14a constituting
bonded magnet 14 is filled toward magnet hole 13 from end face 11c
of rotor core 11 in the direction along shaft center 12a of rotary
shaft 12. Mixture 14a constituting bonded magnet 14 is inserted
from gate 50 included in an insert die.
[0091] As illustrated in FIG. 10, the density of bonded magnet 14
is lower on the side of end face 11d toward which mixture 14a
constituting bonded magnet 14 is filled than on the side (side on
end face 11c) where gate 50 is located. Note that the side of end
face 11d is indicated as a side opposite to gate-side in FIG.
10.
[0092] As apparent from FIG. 10, the density of bonded magnet 14
obtained by curing mixture 14a becomes lower toward the side
opposite to gate-side from the gate-side. The reason of this is
considered, in principle, such that the filling pressure for
mixture 14a constituting bonded magnet 14 is lowered in proportion
to the distance to the gate.
[0093] In view of this, according to the rotor used in the motor
according to the present exemplary embodiment, magnet thickness
.alpha.2 on magnet end part 15 can be adjusted in proportion to the
decrease rate of the density of bonded magnet 14. Specifically,
magnet thickness .alpha.2 is set larger on magnet end part 15 where
the density of bonded magnet 14 is lowered. Magnet thickness
.alpha.2 may be increased in proportion to the decrease in the
density of bonded magnet 14.
[0094] According to this configuration, fluidity of mixture 14a
constituting bonded magnet 14 is enhanced. Therefore, in rotor 10
used in the motor according to the present exemplary embodiment,
the density of bonded magnet 14 can be made uniform, regardless of
the shape of magnet hole 13. Thus, rotor 10 can three-dimensionally
suppress deterioration in magnetic characteristics.
[0095] Particularly, in rotor 10 used in the motor according to the
present exemplary embodiment, magnet thickness .gamma. on the side
of end face 11d of magnet hole 13, at which the density of bonded
magnet 14 obtained by curing mixture 14a is lowered, is increased,
as illustrated in FIG. 8. Specifically, magnet thickness .gamma.
may be increased in proportion to the decrease rate of the density
of bonded magnet 14.
[0096] According to this configuration, fluidity of mixture 14a
constituting bonded magnet 14 is enhanced. Thus, in rotor 10 used
in the motor according to the present exemplary embodiment, the
variation in the density of mixture 14a is reduced more than
conventionally in the region of magnet hole 13 from end face 11c
located on the side of gate 50 to end face 11d located on the side
opposite to gate 50, regardless of the shape of magnet hole 13.
Since the variation in density of mixture 14a is reduced, an
extreme density variation does not occur on bonded magnet 14
obtained by curing mixture 14a. Thus, rotor 10 can
three-dimensionally suppress deterioration in magnetic
characteristics.
[0097] In addition, as illustrated in FIG. 5, rotor 10 used in the
motor according to the present exemplary embodiment satisfies the
following relation with respect to magnet thickness .alpha.2 on
magnet end part 15 and magnet thickness .beta.2 on magnet central
part 16. Specifically, bonded magnet 14 is configured such that
resistance to demagnetization D1 of magnet central part 16 and
resistance to demagnetization D2 of magnet end part 15 become equal
to each other. To make resistance to demagnetization D1 and
resistance to demagnetization D2 equal to each other, bonded magnet
14 is adjusted such that the total amounts of magnet powders
included in the respective parts are equal to each other.
[0098] If resistance to demagnetization D1 and resistance to
demagnetization D2 are equal to each other, the magnetic
characteristics of bonded magnet 14 become uniform.
[0099] That is, in the case where the magnetic characteristics of
bonded magnet vary, it is considered, for example, that
demagnetization occurs on the portion of the bonded magnet where
the magnetic characteristics are deteriorated.
[0100] In view of this, if the magnetic characteristics of bonded
magnet 14 are made uniform as described above, the occurrence of
problems such as demagnetization can be prevented.
[0101] As illustrated in FIGS. 1 and 3, when a current flows
through winding 43 wound around stator 40, a magnetic flux is
generated from winding 43. On the other hand, bonded magnets 14
generate magnetic fluxes of the magnetic components. Magnetic force
generated by the interaction of these magnetic fluxes generates
rotary torque for rotating rotor 10.
[0102] In this case, demagnetizing field is applied to bonded
magnet 14 in the direction of reducing the magnetic flux of bonded
magnet 14 from winding 43 on the portion of magnet hole 13 near the
side of outer circumferential surface 11b. Therefore, bonded magnet
14 is required to increase resistance to demagnetization so as not
to generate demagnetization.
[0103] In principle, the resistance to demagnetization of bonded
magnet 14 increases in proportion to the magnet thickness.
Therefore, the resistance to demagnetization of bonded magnet 14
can be increased by increasing the magnet thickness. However, if
the magnet thickness is increased, the amount of magnet powders to
be used for bonded magnet 14 is increased, which increases
cost.
[0104] In view of this, in rotor 10 in the present exemplary
embodiment, only the magnet thickness of bonded magnet 14 on magnet
end part 15 where demagnetizing field is applied is increased.
Thus, in rotor 10, the magnet thickness of bonded magnet 14 is
increased only on a portion which is required to have increased
resistance to demagnetization. In other words, rotor 10 according
to the present exemplary embodiment enables an increase in
resistance to demagnetization of bonded magnet 14 by increasing
magnet powders at minimum to the optimum portion which is required
to have increased resistance to demagnetization.
[0105] Accordingly, a motor having excellent magnetic
characteristics can be provided at low cost without increasing the
size of motor 100 by using rotor 10 according to the present
exemplary embodiment.
[0106] Note that, in the above exemplary embodiment, the number of
poles of rotor 10 is six. That is, the above exemplary embodiment
indicates that the number of magnet holes 13 is six. The technical
scope of the present invention is not limited to this number. When
n is defined as a natural number, and if the number of poles of
rotor 10 is 2n, the technical scope of the present invention
encompasses rotor 10 having the present configuration.
[0107] In addition, the motor described above has a specification
of 6-pole 9-slot concentrated winding. According to the technical
scope of the present invention, the similar operation and effect
can be obtained, even if other specifications are used. For
example, the technical scope of the present invention encompasses a
concentrated winding motor with other combinations. Further, the
technical scope of the present invention also encompasses a
distributed winding motor or a wave winding motor with respect to a
winding of a slot.
[0108] In addition, similarly, the shape of bonded magnet 14 is not
limited to the above-described shape. For example, the
cross-section of bonded magnet 14 orthogonal to shaft center 12a
may have a V shape or a U shape. If so, the similar operation and
effect can be obtained.
INDUSTRIAL APPLICABILITY
[0109] The interior permanent magnet rotor according to the present
invention and a motor using this rotor are widely applicable to
motors using permanent magnets, such as electrical apparatuses or
industrial machines.
REFERENCE MARKS IN THE DRAWINGS
[0110] 10: rotor (interior permanent magnet rotor) [0111] 11: rotor
core [0112] 11a: steel plate [0113] 11b: outer circumferential
surface [0114] 11c, 11d: end face [0115] 12: rotary shaft [0116]
12a: shaft center [0117] 13: magnet hole [0118] 14: bonded magnet
[0119] 14a: mixture [0120] 15: magnet end part [0121] 15a: end part
[0122] 16: magnet central part [0123] 16a: central part [0124] 17,
18: arc [0125] 17a: convex surface [0126] 18a: concave surface
[0127] 20: d-axis magnetic flux path [0128] 21: q-axis magnetic
flux path [0129] 30: bearing [0130] 40: stator [0131] 41: stator
core [0132] 42: insulator [0133] 43: winding [0134] 44: teeth
[0135] 50: gate [0136] 100: motor
* * * * *